Microvalves and micropumps which have low power, high response speed and high reliability in the presence of mists and particulates in the flow channels have long been sought. Using electrostatic force as the power for the device, devices have been proposed which are expected to operate at high speed, using low power. However, these devices attract mists and particles in the flow channel to the surface of their electrodes by electrostatic force that is produced by those electrodes. This can cause charging of the insulator layer on the electrode surfaces, which in turn can result in permanent sticking of the surfaces and a permanently closed flow channel.
One means for overcoming sticking is the use of more powerful electrostatic forces, which may be applied in both directions. Many such devices also employ a second force, such as pneumatic pressure to actuate the device between an open and closed position.
To accomplish this sort of microvalve or micropump, it has been proposed to use a wafer bonding method to produce a structure having a central pillar connected to both upper and lower electrodes, both of which are conductive. A pillar is generally located above the flow inlet. A center electrode contains passivation on the portion facing the upper electrode, itself held on an insulated electrode holder, such that the pillar moves from one side to the other as electrostatic force is applied to each driving electrode.
The primary drawback from such a design is that it is difficult to construct and maintain in operation because the concept of stacking wafers requires a complicated, expensive manufacturing process using techniques that have not been fully developed. As a result, no such product is available at the present time.
It would be of great advantage in the art if a microvalve could be manufactured that would be bi-directional, operated by electrostatic forces, wherein the electrostatic field itself is enclosed in a sealed volume, thus isolating it from the gas or fluid being controlled.
It would be another great advance in the art if such a device could be prepared without bonding multiple wafers, without assembly and bonding of precisely aligned multiple wafers.
Other advantages will appear hereinafter.